One of the most promising technologies for commercially producing carbon nanostructures such as single wall nanotubes, multi-wall nanotubes, nanofibers, and fullerenes is catalytic chemical vapor deposition (hereinafter “CCVD”). As illustrated in FIG. 1, in a CCVD type reactor, a hydrocarbon gas, or a hydrocarbon/carrier gas combination 10 is introduced into a reaction chamber 20 and passed over a susceptor 30 that contains a metal catalyst 40 heated to a specific temperature. The carrier gas can be nitrogen, argon, hydrogen, or helium. The reaction chamber 20 and the susceptor 30 are normally made from graphite, ceramic, or metal. The heating is achieved by using heating coils 70 wrapping around the reaction chamber 20. The metal catalyst 40 such as Fe, Co, or Ni, causes the hydrocarbon gas to decompose into its component carbon atoms, after which the carbon atoms recombine on the catalytic surface to form carbon nanostructures of various diameters and lengths. However, there are limitations with CCVD type reactor that limit the amount of nanostructures that can be produced at one time.
One of the major limitations of a conventional CCVD type reactor for nanostructure synthesis is the size of a susceptor that can be used. Large size susceptors, desirable for producing large quantities of carbon nanostructures, introduce difficulties in controlling the hydrocarbon gas flow over the catalyst powder bed and attaining tight control of a reaction temperature. It is known that when a hydrocarbon or a mixture of hydrocarbon and carrier gas, also called carbon feedstock or feedstock gas, moves horizontally along the susceptor 30, the catalyst 50 placed at the front end of the susceptor 30 is exposed to the carbon feedstock before the catalyst 60 at the end of the susceptor 30, usually depleting the carbon feedstock gas before it reaches the end of the susceptor 30. The catalyst 60 at the end of the susceptor 30 usually comes into contact with the feedstock gas when the nanostructures growing on the catalyst 50 at the front end of the susceptor 30 can no longer expand. Nanostructures grown in such reactors have large variations in lengths and diameters. Furthermore, the use of conventional ovens results in temperature gradient along the length of the oven. This temperature gradient results in varying temperature conditions that have a significant negative impact on the quality, characteristics, and purity of carbon nanostructures grown therein. Additionally, conventional ovens consume large amounts of energy and heat inefficiently. Because uniform length, diameter, and high purity are desired properties for carbon nanostructure, the performance of CCVD type reactor needs to be improved.
Moreover, long and aligned carbon nanotubes (CNTs) are excellent candidates for many applications such as nano-electronic devices, field emitter transistors (FETs), nano-composite materials with new and improved properties, Silicon based devices and many other similar applications but they are difficult to grow.
Many researchers have tried to grow long CNTs using different methods such as laser ablation, arc discharge and CCVD. Out of all the methods, CCVD has proven to be the most successful for grow of long nanotubes in large scale. In the CCVD method, by controlling the growth conditions one can control the length and morphology of CNTs. Factors such as the nanoparticle catalytic lifetime, the interaction between the nanoparticle and the support, and synthesis conditions strongly influence the length and orientation of long CNTs.
In the past, people tried to grow horizontally aligned CNTs using different catalytic systems utilizing the conventional chemical vapor deposition. Different techniques such as spin coating, electroless plating, sputtering, micro-contact printing, electrospray, and many more have been previously used for catalyst deposition on flat surfaces.
Once long CNTs are grown they can be aligned using different methods such as wet chemical assemblies, high temperature extrusion techniques, electric fields, or using different solution depositions and dielectrophoresis. Usually, these methods are pretty tedious and not very successful. In addition to Fe, other metals such as Co, Mo, Ni and many more or a mixture of two different metals can be utilized as catalytic systems. Straight CNTs were grown on Co—Ni catalyst system but they were not aligned.
Therefore, a heretofore unaddressed need exists in the art to address the aforementioned deficiencies and inadequacies.